Radio frequency (RF) amplifiers are used in a variety of communication systems. A wireless communication system, for example, may require an RF front-end running at frequencies in the Gigahertz (GHz) range. In order to minimize power consumption and filter out unwanted signals and noise at those frequencies, RF amplifiers with inductor-capacitor (LC) tanks are typically used.
In most cases, the gain of an inductor-based RF amplifier is a function of the transconductance of an input transistor and an impedance of an output inductor-capacitor (LC) tank within the amplifier. Usually, the impedance of the LC tank is designed to be much smaller than the transistor output impedance. Consequently, the LC tank tends to dominate the output impedance. At a resonance frequency, the output impedance is inversely proportional to the series resistance associated with the inductor.
Unfortunately, the gain of an RF amplifier can vary significantly as a function of process, temperature, and age variations. In a typical CMOS process, for example, the transconductance and inductor series resistance can vary significantly with process and temperature variations. As a result, the performance of the RF amplifier can vary, resulting in degradation of the performance of the overall communication system.